Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > > > There's one more thing, actually.  If the on-disk data and metadata are
> > > > changed _after_ the sync we do and _before_ we create the snapshot image,
> > > > and the subsequent  resume fails,
> > > 
> > > Well, but this is equivalent to a power failure immediately after the sync, so
> > > there _must_ be a way to recover the filesystem from that, no?
> > 
> > Exactly.
> > 
> > > I think I'll prepare a patch for freezing the work queues and we'll see what
> > > to do next.
> > 
> > Thanks!
> 
> Okay, the patch follows.
> 
> I've been running it for some time on my boxes and it doesn't seem to break
> anything.  However, I don't use XFS, so well ...

Seems like a way to go, thanks!
									Pavel

> Index: linux-2.6.19-rc5-mm2/include/linux/workqueue.h
> ===================================================================
> --- linux-2.6.19-rc5-mm2.orig/include/linux/workqueue.h	2006-09-20 05:42:06.000000000 +0200
> +++ linux-2.6.19-rc5-mm2/include/linux/workqueue.h	2006-11-15 21:58:40.000000000 +0100
> @@ -55,9 +55,11 @@ struct execute_work {
>  	} while (0)
>  
>  extern struct workqueue_struct *__create_workqueue(const char *name,
> -						    int singlethread);
> -#define create_workqueue(name) __create_workqueue((name), 0)
> -#define create_singlethread_workqueue(name) __create_workqueue((name), 1)
> +						    int singlethread,
> +						    int freezeable);
> +#define create_workqueue(name) __create_workqueue((name), 0, 0)
> +#define create_freezeable_workqueue(name) __create_workqueue((name), 0, 1)
> +#define create_singlethread_workqueue(name) __create_workqueue((name), 1, 0)
>  
>  extern void destroy_workqueue(struct workqueue_struct *wq);
>  
> Index: linux-2.6.19-rc5-mm2/kernel/workqueue.c
> ===================================================================
> --- linux-2.6.19-rc5-mm2.orig/kernel/workqueue.c	2006-11-15 21:32:13.000000000 +0100
> +++ linux-2.6.19-rc5-mm2/kernel/workqueue.c	2006-11-15 22:27:40.000000000 +0100
> @@ -31,6 +31,7 @@
>  #include <linux/mempolicy.h>
>  #include <linux/kallsyms.h>
>  #include <linux/debug_locks.h>
> +#include <linux/freezer.h>
>  
>  /*
>   * The per-CPU workqueue (if single thread, we always use the first
> @@ -57,6 +58,8 @@ struct cpu_workqueue_struct {
>  	struct task_struct *thread;
>  
>  	int run_depth;		/* Detect run_workqueue() recursion depth */
> +
> +	int freezeable;		/* Freeze the thread during suspend */
>  } ____cacheline_aligned;
>  
>  /*
> @@ -251,7 +254,8 @@ static int worker_thread(void *__cwq)
>  	struct k_sigaction sa;
>  	sigset_t blocked;
>  
> -	current->flags |= PF_NOFREEZE;
> +	if (!cwq->freezeable)
> +		current->flags |= PF_NOFREEZE;
>  
>  	set_user_nice(current, -5);
>  
> @@ -274,6 +278,9 @@ static int worker_thread(void *__cwq)
>  
>  	set_current_state(TASK_INTERRUPTIBLE);
>  	while (!kthread_should_stop()) {
> +		if (cwq->freezeable)
> +			try_to_freeze();
> +
>  		add_wait_queue(&cwq->more_work, &wait);
>  		if (list_empty(&cwq->worklist))
>  			schedule();
> @@ -350,7 +357,7 @@ void fastcall flush_workqueue(struct wor
>  EXPORT_SYMBOL_GPL(flush_workqueue);
>  
>  static struct task_struct *create_workqueue_thread(struct workqueue_struct *wq,
> -						   int cpu)
> +						   int cpu, int freezeable)
>  {
>  	struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
>  	struct task_struct *p;
> @@ -360,6 +367,7 @@ static struct task_struct *create_workqu
>  	cwq->thread = NULL;
>  	cwq->insert_sequence = 0;
>  	cwq->remove_sequence = 0;
> +	cwq->freezeable = freezeable;
>  	INIT_LIST_HEAD(&cwq->worklist);
>  	init_waitqueue_head(&cwq->more_work);
>  	init_waitqueue_head(&cwq->work_done);
> @@ -375,7 +383,7 @@ static struct task_struct *create_workqu
>  }
>  
>  struct workqueue_struct *__create_workqueue(const char *name,
> -					    int singlethread)
> +					    int singlethread, int freezeable)
>  {
>  	int cpu, destroy = 0;
>  	struct workqueue_struct *wq;
> @@ -395,7 +403,7 @@ struct workqueue_struct *__create_workqu
>  	mutex_lock(&workqueue_mutex);
>  	if (singlethread) {
>  		INIT_LIST_HEAD(&wq->list);
> -		p = create_workqueue_thread(wq, singlethread_cpu);
> +		p = create_workqueue_thread(wq, singlethread_cpu, freezeable);
>  		if (!p)
>  			destroy = 1;
>  		else
> @@ -403,7 +411,7 @@ struct workqueue_struct *__create_workqu
>  	} else {
>  		list_add(&wq->list, &workqueues);
>  		for_each_online_cpu(cpu) {
> -			p = create_workqueue_thread(wq, cpu);
> +			p = create_workqueue_thread(wq, cpu, freezeable);
>  			if (p) {
>  				kthread_bind(p, cpu);
>  				wake_up_process(p);
> @@ -657,7 +665,7 @@ static int __devinit workqueue_cpu_callb
>  		mutex_lock(&workqueue_mutex);
>  		/* Create a new workqueue thread for it. */
>  		list_for_each_entry(wq, &workqueues, list) {
> -			if (!create_workqueue_thread(wq, hotcpu)) {
> +			if (!create_workqueue_thread(wq, hotcpu, 0)) {
>  				printk("workqueue for %i failed\n", hotcpu);
>  				return NOTIFY_BAD;
>  			}
> Index: linux-2.6.19-rc5-mm2/fs/xfs/linux-2.6/xfs_buf.c
> ===================================================================
> --- linux-2.6.19-rc5-mm2.orig/fs/xfs/linux-2.6/xfs_buf.c	2006-11-15 21:32:08.000000000 +0100
> +++ linux-2.6.19-rc5-mm2/fs/xfs/linux-2.6/xfs_buf.c	2006-11-15 22:12:43.000000000 +0100
> @@ -1826,11 +1826,11 @@ xfs_buf_init(void)
>  	if (!xfs_buf_zone)
>  		goto out_free_trace_buf;
>  
> -	xfslogd_workqueue = create_workqueue("xfslogd");
> +	xfslogd_workqueue = create_freezeable_workqueue("xfslogd");
>  	if (!xfslogd_workqueue)
>  		goto out_free_buf_zone;
>  
> -	xfsdatad_workqueue = create_workqueue("xfsdatad");
> +	xfsdatad_workqueue = create_freezeable_workqueue("xfsdatad");
>  	if (!xfsdatad_workqueue)
>  		goto out_destroy_xfslogd_workqueue;
>  

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html